Countries have signed the Paris agreement on climate change to limit the rise in global temperatures to well below 2 degrees Celsius (3.6 degrees Fahrenheit) above pre-industrial levels, and ideally to 1.5C.

An increase of 3C or 4C could raise mortality rates by between 1 and 9 percent, according to a study published in the journal Climatic Change.

“Currently, we are on a trajectory to reach over 3 degrees Celsius of warming, and if this trend continues there would be serious consequences for health in many parts of the world,” said co-author Antonio Gasparrini in a statement.

Southeast Asian nations like the Philippines and Vietnam would be most affected by heat-related mortality, along with those in Southern Europe and South America, according to the report.

A drop in cold-related deaths elsewhere would not be enough to offset overall increase, said researchers led by scientists from the London School of Hygiene & Tropical Medicine who looked at 23 countries for the survey.

A nudge in global temperatures from 1.5C to 2C would likely result in less than a 1 percent increase in related deaths in warmer regions such as Southern Europe, South America and Southeast Asia, they said.

The study did not take into account measures to adapt to rising temperatures, or demographic and economic factors, but those could have an impact when it comes to reducing heat-related deaths, said lead author Ana Maria Vicedo-Cabrera.

“Evidence so far suggests that we are adapting to heat, so we expect that in the future, maybe, the mortality risk due to temperatures could be lower compared to today, but still it’s not clear,” Vicedo-Cabrera told the Thomson Reuters Foundation.

United Nations Secretary General Antonio Guterres warned this week it could be too late to stop “runaway climate change” unless countries take action by 2020 to reduce global warming.